"No user data was at risk and we have restored full access to the site for most users," she added. " We’re continuing to monitor the situation to ensure that users have the fast and reliable experience they’ve come to expect from Facebook."

If Facebook was attacked by the same party or parties who drove Twitter offline today, as seems likely, it means two things: First, Facebook is more resilient to denial-of-service attacks than Twitter is; and second, someone – or something – really wants both Facebook and Twitter offline today.